1. Field of the Invention
This invention relates to a magnetic head in which the amount of induced noise is reduced for the noise magnetic flux entering from the front of the magnetic gap.
2. Description of the Prior Art
Generally, a magnetic head encounters a situation that during recording or reproduction, induced noise is produced by a noise magnetic flux generated from a tape driving motor, terrestrial magnetism or other external instrument and such induced noise mixes with the regular output information from a magnetic recording medium such as a magnetic tape or the like to thereby prevent accurate information from being obtained. In the magnetic head, therefore, the core thereof forming a magnetic circuit is usually surrounded by a shield case so as to be magnetically isolated from the outside and protected against the noise magnetic flux. However, from the viewpoint of the structure of the magnetic head, the magnetic gap portion of the core must be brought into direct or indirect contact with a magnetic recording medium such as a magnetic tape or the like and therefore, the surface of the core which is in contact with the magnetic recording medium is exposed from the shield case. Thus, such surface of the core is the greatest weak point in magnetically shielding the magnetic head. FIGS. 1A-4A of the accompanying drawings show typical constructions of conventional magnetic heads in which a coil 2 is wound on a core 1 forming a magnetic circuit and the core is surrounded by a shield case 3, and FIGS. 1B-4B which correspond to FIGS. 1A-4A show the amount of induced noise flowing through the coil 2. In FIGS. 1A-4A, the core is protected by the shield case 3 against the magnetic flux entering from the X-axis direction, while against the magnetic flux entering from the Y-axis direction (from the front of the magnetic gap), the core is unavoidably subjected to the influence from the open portion 3a of the shield case 3 because the portion S of the core 1 which is contacted by the magnetic recording medium is exposed. Accordingly, a magnetic head of a construction that has a minimum amount of induced noise in the Y-axis direction is more advantageous in that it is less susceptible to the influence of the noise magnetic flux.
FIG. 1A shows a half wind system which is structurally simple (a coil 2 is wound only on one side of a core 1), but as regards the induced noise, this system is disadvantageous because the maximum value of induced noise lies in the Y-axis direction as shown in FIG. 1B.
FIG. 2A shows a balance wind system (coils 2 are wound on both sides of a core 1 in opposite directions) and this is an advantageous structure in which the induced noise assumes a minimum value in the Y-axis direction as shown in FIG. 2B. However, this system requires two coils and an intermediate connecting lead wire for connecting the two coils, and this results in disadvantages such as increased cost of parts, complexity of assembly and an increased number of assembling steps.
FIG. 3A shows a back balance wind system (coils 2 are wound on the both lower portions of a core 1) and this system is excellent in that as in the balance wind system of FIG. 2A, the induced noise in the Y-axis direction assumes a minimum value as shown in FIG. 3B, but it suffers from disadvantages such as complexity of assembly, an increased number of assembling steps and increased cost of parts.
FIG. 4A shows a back half wind system (a coil 2 is wound only on one lower portion of a core 1) which, as compared with the balance wind system of FIG. 2A and the back balance wind system of FIG. 3A, is structurally very simple and the coil need not be directly wound on the core, but a separately prepared coil 2 may be inserted over one half of the core 1 and this leads to reduced cost of manufacture. However, as shown in FIG. 4B, the maximum value of induced noise approaches the Y-axis direction and therefore, as compared with the systems of FIGS. 2B and 3B, the amount of induced noise is great (the induced noise characteristic is bad).
Thus, in order to reduce the amount of induced noise, it has heretofore been unavoidable to adopt the balance wind system or the back balance wind system in spite of increased cost of manufacture.